Aggressive media exposed differential pressure sensor with a deposited membrane

A new piezoresistive differential pressure sensor design for harsh wet environments is presented. The sensor design is based on a deposited membrane, which is deposited on top of polysilicon interconnects and piezoresistors. Flat membrane surfaces are thereby achieved. This enables thin film protective coating using sputtered films, which usually have poor step coverage. The concept is demonstrated using both epipoly silicon and sputtered amorphous silicon as membrane materials and tantalum oxide as coating material. Using polysilicon piezoresistors, a sensitivity of 11.3 mV/V bar was obtained. Exposure of the sensors with sputtered amorphous silicon membranes to aggressive media with pH 11 and 70/spl deg/C for 20 hours did not change their performance.